why does exec-shield load .so @ diff addrs run to run

From: Eric Taylor (et1_at_rocketship1.com)
Date: 04/28/04 

Date: Wed, 28 Apr 2004 15:44:20 GMT

We have started trying out Fedora and have found that with exec-shield enabled (value=1) the load address of some .so libraries keep
moving around (slightly) from run to run. I was wondering why this should happen. Why isn't the algorithm deterministic? We have
been forced to turn it off, because it breaks our fast memory checkpoint/restart algorithm which depends on program libraries
loading into memory at the same place fro run to run.

I have seen a .so file load a few 10's of k bytes higher or lower, even leaving a small holes between adjacent .so loads.

I understand the ascii-armor trick, and a little bit of how exec-shield tracks high segment addresses, and I do understand the
desire to keep the stack from being executable, but I didn't see anything that would explain why it should work differently from run
to run. Is this supposed to happen?

Relevant Pages

  • Re: [PATCH RFC]: New termios take 2
    ... termios presented by glibc already differs from the termios presented by ... and moving towards a system where we actually _mean_ it. ... C libraries that are important here. ... So if you want to unexport those headers and make sure the C libraries ...
    (Linux-Kernel)
  • RE: HEADS UP: dynamic root support now in the tree
    ... > Aan: current@FreeBSD.org ... >> tweaking and moving around libraries and such dangerous equipment as ...
    (freebsd-current)
  • Re: Protel 99 SE and MS Vista library problem?
    ... not just try to change the permissions on the individual ... Moving the libraries is no problem, you simply have to reload the ... So far I've changed the Protel security settings inside Program ...
    (sci.electronics.cad)
  • Re: gcc linking issue
    ... of other libraries. ... Certainly write, fcntl, et al are defined in libc. ... Try adding another -lc at the end of the link line or moving the ...
    (comp.unix.solaris)
  • objects vs library
    ... I have been moving some of my frequently used components (which are now ... compiled and linked for each application) into libraries, ... The strange ... executables which would indicate that information is duplicated ...
    (comp.programming)